The gills give the earliest clues
An axolotl's three pairs of external gills are its most honest signal. On a relaxed, healthy animal the stalks stand out from the head with full, fine filaments that wave gently in the current. Stress changes them in recognisable ways: the stalks curl forward toward the face — the classic curled-gill posture — or the filaments shrink and thin so the gills look stubby and pale. Gills pressed flat or held at odd angles, especially paired with a curled tail tip, are a stronger warning than either sign alone. Because gills also respond to water movement, compare like with like: look at the gills when the filter flow and lighting are as they usually are, and notice whether the change lasts beyond a few minutes rather than flashing past during a startle.
Behaviour and body signs
Beyond the gills, a stressed axolotl often goes off food it normally takes eagerly, or spits out worms it would usually swallow. Some become restless, swimming repeatedly at the glass or floating at the surface; others do the opposite and hide pressed into a corner or cave for far longer than their normal pattern. Body signs can include a tail tip that curls into a hook, skin that looks patchy, pale or unusually red, a heavier slime coat than usual, or small white fuzzy patches on the gills or skin. One quiet day after a big water change can be simple settling; the concern is a cluster of signs — curled gills plus refused food plus hiding — or any sign that persists across several days without an obvious cause you have already fixed.
Check the water before anything else
Most axolotl stress traces back to the water, so test before you change anything else. Axolotls are cool-water animals that suffer as temperatures climb toward the range where many tropical tanks sit; a thermometer reading is the first number to check. Test the water for ammonia, nitrite and nitrate as well — a cycling hiccup, a clogged filter or decaying uneaten food can push readings up in a tank that looked stable last week. Note recent changes too: a new tank-mate, brighter lighting, stronger filter flow, a moved hide, or a water change done with water at a very different temperature. Write down the readings and the time you took them, fix the cause you find — cooling, a partial water change with treated water matched in temperature, removing waste — and then watch whether the gills relax over the following day.
When it is time for a vet
Contact an exotics or aquatic vet if the axolotl refuses food for several days running, if the gills shrink or develop fuzzy growths, if skin lesions, swelling or bloating appear, or if the animal floats uncontrollably or cannot stay down. Fungal-looking patches, injuries, and stress signs that continue after water readings have been corrected all deserve professional eyes, because an axolotl that looks only mildly off can decline quickly. Take your log: temperatures, test results, feeding notes and when each sign appeared, plus a clear photo of the gills. Keeping that record in your axolotl's KinsLe Pet Passport means the pattern of readings and symptoms is ready to hand over instead of reconstructed from memory at the clinic.